2 A student carried out an experiment to measure the percentage oxygen in the air by using the rusting of iron. The experimental set-up is shown below,
The initial reading on the measuring cylinder was 95 cm, They let the
apparatus for 2 days and the new reading on the measuring cylinder was
80 cm
-iron filings
-measuring cylinder
air
-water
90
100
a Calculate the percentage oxygen in the air using this data.

is there multiple choice answers?

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the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

the answer is c i took the test